1. Field of the Invention
The present invention is directed to a structure of a display device for preventing electromagnetic interference (EMI). The display device comprises a display panel with a plurality of pixels formed between substrates.
2. Background of the Invention
Many conventional display devices such as a plasma display device and others employ an electromagnetic shield as a measure against EMI so that an electromagnetic wave generated by the display devices would not have an undesirable effect on various adjacent control circuits or communication systems.
FIG. 16 shows a sectional structure of a display device 100 comprising such a display panel. One example of a display panel 10 (hereinafter referred to as a panel) is an AC type plasma display panel (PDP). As shown in FIG. 16, in order to electromagnetically shield the display device 100, the panel 10 and a drive circuit substrate 12 equipped with a drive circuit for driving the panel 10 are disposed within a conductive shielding case 20 made of metal. In the conductive shielding case 20, a holding board 15 is provided on a non-display surface side of the panel 10 (below the broken line in the figure), which is opposed to a display surface 10a, to hold the panel 10 made of a glass substrate or the like. The panel 10 and the drive circuit substrate 12 are connected by a wiring board 14 including signal wiring, such as a flexible printed circuit (FPC). The wiring board 14 is also deposited within the conductive shielding case 20.
If the conductive shielding case 20 totally covers the whole surfaces of the panel 10 and the drive circuit substrate 12 which is the biggest source of noise, a reliable electromagnetic shield becomes possible. In the display device as shown in FIG. 16, however, the conductive shielding case 20 does not cover the display surface of the panel 10 which is thus covered by a transparent or translucent conductive filter 18 to be electrically connected to the conductive shielding case 20. By surrounding the panel 10 and the drive circuit substrate 12 with the conductive shielding case 20 and the conductive filter 18, an electromagnetic noise emitted outside the display device 100 is excluded.
Employed as the conductive filter 18 for covering the display surface of the panel 10 is, for example, a glass or acrylic filter with a transparent conductive film, such as an indium tin oxide (ITO) film or a considerably thin silver evaporation film, formed on the internal or external surface thereof, or a filter with fine conducting wires formed lengthwise and crosswise with a small pitch, that is, a filter with a fine wire gauze laminated thereto.
Though conductive, the transparent conductive film such as an ITO has a higher electrical resistance compared to a metal material such as the conductive shielding case 20, thereby providing less shield effect. Thus, in order to reduce the electrical resistance and increase the shield effect, the transparent conductive film needs to be thicker. However, the increased film thickness of the transparent conductive film deteriorates transmittance of light. This reduces display brightness or contrast, thereby reducing display quality. Further, it takes time and increases manufacturing cost to form a thick transparent conductive film.
The fine wire gauze, on the other hand, causes low transmittance of light, and in some cases, generates moire"" on the display surface side in relation to a dot pitch of each pixel of the panel 10. Thus, in this case, it is difficult to prevent deterioration in display quality.
A first aspect of the present invention is directed to a display device having a display panel with a plurality of pixels formed between a pair of substrates and giving a desired display by controlling each of the pixels. The display device comprises: a conductive shielding case with the display panel and a drive circuit for driving the display panel disposed therein, the conductive shielding case having an opening at the side of a display surface of the display panel; and a conductive member disposed between the drive circuit and the display panel. The drive circuit is disposed in the side of an non-display surface of the display panel formed within the conductive shielding case, and the conductive member and the conductive shielding case are connected to provide an electromagnetic shield to the drive circuit.
Preferably, according to a second aspect of the present invention, the display device of the first aspect further comprises a conductive portion having a ground potential; and a signal wire for electrically connecting the drive circuit and the display panel. The conductive portion and the signal wire make a static capacitance.
Preferably, according to a third aspect of the present invention, the display device of the second aspect further comprises an insulating layer formed on the signal wire: and a conductive layer formed on the insulating layer. The conductive layer is forced to have a ground potential.
Preferably, according to a fourth aspect of the present invention, the display device of the third aspect further comprises a connecting means for connecting the conductive layer to the conductive shielding case so that the conductive layer is forced to have a ground potential.
Preferably, according to a fifth aspect of the present invention, the display device of the second aspect further comprises insulating films covering top and bottom surfaces of the signal wire, respectively; and conductive layers formed on each of the insulating films. The conductive layers are forced to have a ground potential.
Preferably, according to a sixth aspect of the present invention, the display device of the second aspect further comprises insulating films covering top and bottom surfaces of the signal wire, respectively; and conductive layers formed on each of the insulating films. One of the conductive layers, disposed at the side of the conductive member disposed between the drive circuit and the display panel, is connected to the conductive member, while the other disposed at the side of the conductive shielding case is connected to the conductive shielding case.
Preferably, according to a seventh aspect of the present invention, the display device of the fifth or sixth aspect further comprises a variable-shape member having conductivity at least on the surface thereof and deposited at least between the conductive layer and the conductive shielding case. The conductive member and the conductive shielding case are electrically connected with the variable-shape member.
Preferably, according to an eighth aspect of the present invention, the display device according to either of the first to third aspects further comprises a noise filter inserted into paths of a power wire and a signal wire extracted from the drive circuit to the outside of the conductive shielding case; and an inductance component added to a grounded wiring path for electromagnetically shielding each of the power wire and the signal wire
A ninth aspect of the present invention is directed to an AC type plasma display panel comprising: a pair of substrates; a plurality of discharge pixel cells formed between the pair of substrates; and a pair of sustain electrodes formed on one of the pair of substrates, to which sustain pulses are applied to control discharge at each of the plurality of discharge pixel cells so as to alternatively reverse polarity between the pair of sustain electrodes to make an instantaneous average voltage almost constant at the pair of sustain electrodes during a sustained discharge period for each of the discharge pixel cells.
Preferably, according to a tenth aspect of the present invention, the display device according to either of the first to ninth aspects further comprises a transparent conductive layer formed on a display surface of the display panel. The transparent conductive layer is connected to the conductive shielding case.
According to the present invention, the conductive shielding case, the conductive member, and the connecting means for connecting the conductive shielding case and the conductive member provide a reliable electromagnetic shield to the drive circuit. This makes it possible to omit an electromagnetic shielding member on the display surface side of the panel, thereby achieving an electromagnetic shield without deterioration in display quality.
Further, since the static capacitance is included between the signal wire and the conductive portion having a ground potential, it becomes possible to prevent noise generated at the drive circuit from being transmitted through the signal wire to the panel and leaked out from the display surface side of the panel.
Further, by forming the insulating layer on the signal wire and the conductive layer on the insulating film, and forcing the conductive layer to have a ground potential, it becomes possible to provide a static capacitance between the signal wire and the conductive portion having a ground potential without connecting the static capacitance element with every signal wire. This results in easy achievement of the circuit.
Further, if the conductive layer forming the static capacitance along with the signal wire is connected to the conductive shielding case by the connecting means, the conductive layer would certainly have a ground potential without floating electrically.
Moreover, if the conductive layers are formed on the insulating layers which cover the top and bottom surfaces of the signal wire, respectively, and they are connected, for example, to the conductive shielding case to apply a ground voltage, an emission of noise from the signal wire itself can be prevented.
Further, the top and bottom surfaces of the signal wire are covered by the insulating layers, respectively, on which a conductive layer is formed. Then, one of the conductive layers, disposed on the side of the conductive member formed between the drive circuit and the display panel is connected to the conductive member, while the other disposed on the side of the conductive shielding case is connected to the conductive shielding case. Thus, those conductive layers act as relay points of the connecting means. This reduces a gap on the shield surface surrounding the drive circuit, thereby improving shield effect.
If the conductive layers formed on the top and bottom surfaces of the signal wire are connected to, for example, the conductive shielding case by a variable-shape member, a gap on the shield surface of the driving circuit can be reduced. This prevents transmission of noise through the signal wire to the panel, and further certainly prevents emission of noise from the signal wire itself.
Further, according to the present invention, a noise filter is inserted into the paths of the power or signal wire, and an inductance component is provided into the path of the ground wire for electromagnetically shielding the power and signal wires. This certainly prevents emission of noise from antennas of the panel and the ground wire extending to the outside of the shield, even if the conductive shielding case fails to completely surround the display surface of the panel.
Moreover, by driving so as to make the instantaneous average voltage constant at the pair of sustain electrodes during the sustained discharge period, generation of noise itself can be reduced in the plasma display panel.
In addition to the above-described structure, if a transparent conductive layer is such thin or formed of such a material as not to affect the display quality, a more reliable electromagnetic shield can be achieved in the display device.
The object of the present invention is to provide a display device achieving a reliable electromagnetic shield without deterioration in display quality.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.